On Mon, 8 May 2006 21:54:53 +0200
Wolfgang Hoffmann <woho@email-addr-hidden> wrote:
> > I browsed over that page and didn't find any info on setting up the irq
> > handler priorities which is _the_ essential feature of -rt.
>
> Apropos: on your page on -rt setup (excellent page, btw., many thanks! :-),
> you suggest raising "softirq-timer/0" to prio 99, to make sleep() function
> right (http://tapas.affenbande.org/?page_id=40 sleep() based/system timer).
>
> I did so, and got strange latencies (> 40 ms) exactly once every 10 minutes,
> caused by some routing-related action (rt_secret_rebuild) being run by the
> softirq-timer/0 thread. Don't you get bit by that, too? Kernel is 2.6.16-rt16
I haven't been bitten by that. Do you also get xruns with [i suppose so,
just asking to make sure]? I haven't had as much time as before to play
around and test things, so maybe it has crept into the kernel recently
or maybe i just always had high-res timers enabled.
> My solution is to configure with CONFIG_HIGH_RES_TIMERS=y. Then, sleep() wakes
> up correctly even with softirq-timer/0 being low-priority (SCHED_FIFO 1 or
> even SCHED_OTHER).
>
> In general I find adjusting priorities of the various softirq kernel threads a
> bit of secret art. I can't find much documentation about "what kernel thread
> runs which job" that would help making some proper decisions here. I found my
> desktop "feels" most responsive when demoting all softirq thread to
> SCHED_OTHER. I did so after seeing that with a non-rt kernel, bottom-half
> handler don't run SCHED_FIFO/_RR at all. So -rt now gives me robust low
> latencies for jackd, and still proper desktop feeling.
>
> Well, maybe this is getting off-topic for this list. But it seems to me
> trimming priorities between kernel and userland threads is a bit like no
> man's land.
I agree. Maybe Lee Revell knows more [CC'ing him]. Lee, you know
something about all these softirq threads? What exactly do they do?
Regards,
Flo
-- Palimm Palimm! http://tapas.affenbande.orgReceived on Tue May 9 08:15:02 2006
This archive was generated by hypermail 2.1.8 : Tue May 09 2006 - 08:15:02 EEST